The present invention relates to golf club shafts, in particular metal or metal matrix composite golf club shafts, which have been produced by a process that includes a hydroforming step. By utilizing a hydroforming step, a golf club shaft can be constructed having a variety of forms or shapes heretofore not possible. Advantageously, the hydroformed shafts can be configured to enhance club feel or performance, or even to include hydroformed ornamental design elements which can be located in any or all of a tip, grip, or intermediate sections of the shaft.
The prior art golf clubs and shafts thereof have a degree of flexibility that is greatly dependent on the shaft material. Each individual golfer, especially a skilled player, has a preference for certain characteristics, such as feel, in a golf club or set of clubs. Generally feel is measured by the flexibility of the golf club shaft. One golfer may prefer a stiff feel, while others may prefer a more flexible club. Flexibility of golf club shafts can even vary from one section of the shaft to another, such as in the tip, butt, and intermediate sections.
U.S. Pat. No. 5,620,380 to Tennent et al. relates to a light weight golf club shaft described as having a xe2x80x9cmodified hourglassxe2x80x9d shape which provides many predetermined combinations of flex, stiffness and torque which together are perceived as shaft and club xe2x80x9cfeel.xe2x80x9d The shaft reportedly reduces shaft weight to the level desired by a golfer by using a substantially uniform shaft wall thickness while maintaining the unique xe2x80x9chour glassxe2x80x9d external profile of our previous shaft. The shaft is formed of a base with axial sections: a grip section, an upper flare section, a flex control section, a lower flare section, and a hosel section, the whole forming an exterior shaft profile. The shaft may be made from metal such as steel, titanium, aluminum or their alloys, or composites formed of reinforcing fibers and polymeric materials. The preferred fibers for reinforcement are the carbon, ceramic, metallic, glass, aramid and extended chain polyethylene fibers, most preferably the carbon fibers. Preferred among the polymers which may be used are thermosetting resins such as the phenolics, polyesters, melamines, epoxies, polyimides, polyurethanes and silicones. The shafts reportedly may be produced by a variety of methods, including casting, molding (as around one or more mandrels), expanding or drawing.
U.S. Pat. No. 6,071,460 to Renaudin et al. relates to an apparatus for manufacturing a reinforced golf club shaft having a complex shape. An inflatable bladder is positioned over a mandrel having a simple shape. Layers of fiber material are then rolled over inflatable bladder to produce a sub-assembly. The sub-assembly is placed in a mold defining a negative of the shape of the final shaft that is to be produced. The impression may have enlarged or narrowed regions for producing irregularities in the shape of the shaft. The bladder is expanded within the mold so that the composite structure is radially displaced and compressed between the bladder and the mold. The inflatable bladder has a variable thickness that conforms to the shape of the impression so that the composite structure undergoes a uniform and minimum displacement along its entire length, which reportedly improves the mechanical properties of the final shaft.
U.S. Patent Application Publication No. 2001/0014626 to Takiguchi et al. relates to a golf club shaft and a method especially suited for producing the shaft that reportedly provides high rigidity and ease of use and that allows inexpensive and easy manufacture. A sloped section 16 expanding toward a grip end 14 is formed. The sloped section has a slope gradient of 15/1000-35/1000 and a length of 200-350 mm. The outer diameter of the grip end is 18-25 mm. On the side of the sloped section toward an end 18, there is formed a semi-sloped section 19 with a slope gradient of 4/1000-13/1000. A kick point is formed at a position 40-46% from the small-diameter end relative to the shaft length.
The prior art golf club shafts and processes for making the same have been limited in design and functionality by their production devices. The golf club shafts of the present invention overcome the aforementioned problems.
The present invention relates to a golf club shaft, a set of shafts, or golf clubs formed from the shafts of the present invention and a method of production therefore. The shafts are produced by a process which includes a hydroforming step, wherein the shaft is expanded by fluid to fit the dimensions of a hydroform mold.
The shafts of the present invention are generally produced by the following process. First, a tube is formed by any of a number of procedures. In one method, a planar piece of metal is formed and welded into a tube. Alternatively, a seamless tube can be formed by an extrusion process. The tube is subsequently annealed at least once. Preformed or manufactured tubing could be otherwise be utilized. The tube is drawn over a number of mandrels producing a shaft blank. The shaft blank can have any number or multitude of thicknesses, i.e. generally from 1 to about 10 and preferably from 1 to about 6, with a constant outer diameter at this point in the process. The shaft is then end formed by compressing the tube axially through a series of cylindrical dies, the inside diameters of the dies being less than the shaft outer diameter, to produce a stepped blank. A stepped blank generally has grip and tip sections with constant outer diameters and an interconnecting section which optionally may contain numerous steps or gradations from a larger diameter progressively to a smaller diameter. The shaft generally has exterior dimensions which are slightly smaller than that of the female hydroform mold utilized in the hydroforming process. The shaft is placed into a hydroform mold and fluid is introduced into the shaft wherein the pressure therefrom causes various portions of the shaft to expand outward and contact the mold surfaces. Advantageously, shafts with variable outer and/or inner diameters and variable wall thicknesses, and/or nonprogressive modifications can be formed. The hydroformed shaft is cut to length and finished with optional steps such as heat treating, polishing and plating.